ON MARINE EOILERS.

The boiler was a vertical one, 30 feet high,with two large flues through it, and the feedwater was originally injected at the bottom,impinging upon the flue; and the pitting ofthe plates took place for a length of 3 feet fromthe entrance of the feed. But by altering thefeed pipe to enter at the centre of the boilerand furnishing it with a rose jet to distributethe feed water gradually, the corrosion wascompletely stopped at once.” He enquiredwhether it had been found that there was anyparticular way of supplying the feed water inthe boilers described in the paper, in order todiminish the corrosive effects.

Mr. D. Bollo replied, that “ he had not foundthat the place where the feed was introducedin the boilers had any perceptible connectionwith the corrosion : the feed pipes had beenaltered to different positions in several of theboilers described in the paper, and in somehad remained unaltered, but without affectingthe corrosion; and the corrosive action seemedto have no special effect at the parts nearestthe entrance of the feed, but the pittingseized upon one plate and another indiscrimin-ately and with considerable spaces between.Priming no doubt was effected by the positionof the feed entrance ; and in one of the vesselsthat they had fitted with the surface condensers,having round tubular boilers, much troublehad been experienced from priming, in conse-quence of the feed being injected too nearthe point where the steam was taken off; butby putting the feed pipe lower and at the backof the boiler, the priming was now got rid ofcompletely. He did not think the corrosionof the boiler plates was caused by greasecontained in water: but it seemed more

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probable that, by constantly boiling the samewater over and over again, it was robbed ofsome of its original properties, or becameotherwise altered in quality thereby, so as toproduce the serious effects that were ex-perienced.

Since this evidence, from the various authori-ties now quoted, much has been done in theway of research and reformation, and theresult has been successful. Before, however,entering into this subject, a further noticewill be given to the “ action of the distilledwater on the boiler plate.”

Surface condensers are for the most partcomposed of brass tubes in the present day,this, as much for practical purposes as theo-retical. Brass tubes can be drawn out withoutseam, also the action of the fluid on them doesnot displace much of the entire nature of thematerial. Now a copper tube—although thebetter conductor of heat and cold—is moreexpensive in manufacture and use than brass,and does impart more of its nature to thefluid during the passage of the same than theformer material. Practical evidence is oftenseen as to the truth of this, that where copperand wrought iron are in contact a galvanicaction ensues, and the latter material succumbsto the power of the former. It is obviousthen, that the condensing tube—if of brasseven—must be robbed of some of its copperproperties during the act of condensation,and the fluid is impregnated with the same.On the water entering the boiler a galvanicaction ensues, similar in principle to thatproduced by the actual contact of copperand iron.

Next must be noticed the form assumed

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